JPS6334764B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for recovering pigments by color from waste ink. Inks used in various types of printing, such as letterpress, intaglio, offset, and gravure, generally contain pigments, resins,
It consists of additives such as a solvent and a plasticizer, and as schematically shown in FIG. 1, it is thought that pigment particles 1 are uniformly dispersed in a solvent 3 with a resin 2 interposed therebetween. These pigment particles are broadly classified into extender pigments, inorganic pigments, and organic pigments, each of which has physical properties as shown in Table 1.

【table】

[Table] Note that it goes without saying that appropriate additives such as solvents, resins, and plasticizers are used depending on the type of pigment mentioned above. The hues of new inks are broadly classified into red, blue, yellow, white, and black, and depending on the purpose, they are used alone or in combination of two or more colors. By the way, ink that has become black and dull and can no longer be used, as well as waste liquid after cleaning printing machines, etc.
A large amount of waste ink is discharged from ink manufacturing processes, printing factories, etc., and each waste ink is a mixture of inks of various hues, and the dull colored waste ink includes black ink made of carbon black, Contains blue ink consisting of phthalocyanine blue. It is difficult to recover valuable materials such as pigments and solvents from the above waste ink, and conventionally, most of it has been incinerated or dumped, and in rare cases, hot air, steam, etc. have been injected into the waste ink to dissipate the solvent. , recovery using a condenser, etc. was possible, but sufficient recovery could not be achieved. The inventors of the present invention have repeatedly studied methods for recovering pigments from waste ink, and have obtained the following knowledge. First, the pigment particles used in the inks shown in Table 1 show different dispersibility depending on the type of solvent, as shown in Table 2.

【table】

[Table] ○ Good dispersibility
△ Slightly good dispersibility
× Poor dispersibility Next, as mentioned above, when pigment particles are used in ink, a resin (2 in Figure 1) is used, but depending on the type of resin, the dispersibility in Table 2 is as follows. to come in different ways. (1) Aromatic hydrocarbons such as toluene and xylene are
As shown in Table 2, none of the pigments is dispersed and tends to settle, and this tendency does not change regardless of the type of intervening resin. (2) With ethers such as methyl cellosolve and ketones such as cyclohexanone, all pigments are well dispersed as shown in Table 2, and this tendency does not change regardless of the type of intervening resin. (3) As shown in Table 2, esters such as ethyl acetate, alcohols such as methyl alcohol, ethyl alcohol, and isopropyl alcohol exhibit selectivity in dispersibility depending on the type of pigment, and also depending on the type of intervening resin. For example, methyl alcohol, ethyl alcohol: When the intervening resin is an alkyd resin, these alcohols have no effect of dissolving the alkyd resin, so regardless of the type of pigment, the dispersibility is poor. In the case of nitrocellulose, these alcohols have the effect of dissolving nitrocellulose, so they show the same dispersibility as shown in Table 2. Isopropyl alcohol: Regardless of whether the intervening resin is an alkyd resin or nitrocellulose, isopropyl alcohol has the effect of dissolving nitrocellulose. Ethyl acetate: Ethyl acetate has the effect of dissolving these resins, regardless of whether the intervening resin is alkyd resin or nitrocellulose. , shows dispersibility similar to Table 2, and shows selectivity in dispersion as shown in Table 2. Based on the above findings, it has been found that by adding a solvent with poor pigment dispersibility to waste ink, the dispersibility of pigment particles can be lowered and the pigment particles can be precipitated and separated. Therefore, the present inventors conducted further research on recovering pigments using a solvent with poor pigment dispersibility, and found that if the solvent is applied as an upward flow, the pigment particles will be recovered due to the difference in the floating speed or settling speed of the pigment particles. Separation by color is possible, however, if a large amount of intervening resin is included in the pigment during separation and recovery, there is a storage problem (among the intervening resins, nitrocellulose in particular poses a risk of ignition during storage). Therefore, the present invention was achieved based on the discovery that the above-mentioned solvent needs to have good solubility in resins. That is, in the present invention, when recovering pigment from waste ink, a solvent having poor pigment dispersibility but good solubility in resins is applied to the waste ink in an upward flow in the dispersion tower, thereby increasing the floating or settling speed of pigment particles. This invention relates to a method for recovering each pigment from waste ink according to color, which is characterized by sieving into multiple layers of each pigment in a liquid phase based on differences in color, and extracting and recovering each layer separately. In the method of the present invention, the solvent that gives an upward flow (that is, a solvent that has poor pigment dispersibility but good solubility for resins) (hereinafter referred to as an upward flow solvent) is toluene, xylene, etc., as is clear from Table 2. Among the intervening resins, aromatic hydrocarbons are not very soluble in nitrocellulose, so as mentioned above, they show good solubility in nitrocellulose.
In addition, aromatic hydrocarbons mixed with esters such as ethyl acetate, which do not have very good pigment dispersibility, are used. This mixing ratio is set to aromatic hydrocarbon/esters = 90/10 to 10/
It is preferable to set it as 90 (capacity ratio). Hereinafter, the method of the present invention will be explained in detail with reference to the accompanying drawings and the like. FIG. 2 is a system diagram showing an embodiment of the method of the present invention. In FIG. 2, waste ink is supplied from line 2 to a mixing tank M with its flow rate adjusted by a flow meter _F3 . A solvent for diluting waste ink (hereinafter referred to as dilution solvent) is sent to the mixing tank M from a tank T ₃ by a pump P ₂ and the flow rate is adjusted by a flow meter F ₂ . This diluting solvent lowers the viscosity of the waste ink, making it easier to feed the waste ink to the dispersion tower D, which will be described later, and also serves to uniformly distribute the waste ink in the dispersion tower D. Since it is necessary that the waste ink does not coagulate or precipitate in the mixing tank M, a solvent that has good pigment dispersibility and does not coagulate resins (that is, has good solubility for resins), For example, ketones such as cyclohexanone and methyl isobutyl ketone, and ethers such as methyl cellosolve can be used. The flow rates of the diluting solvent and waste ink are adjusted by the above-mentioned flowmeters F ₂ and F ₃ so that the diluting solvent/waste ink=0.1 to 3 (volume ratio). Setting the volume ratio of diluent solvent/waste ink in this way is such that if it is less than 0.1, there is no point in mixing the diluent solvent, and if it is more than 3, not only will the amount of subsequent processing become large;
This is because a value of 3 or less is sufficient to lower the viscosity. The waste ink mixed with the diluent as described above is sent to the dispersion column D. The above-mentioned ascending solvent is sent to the dispersion column D from the bottom of the column at a constant speed and is given as an ascending flow, and the pigment particles in the waste ink are dispersed due to the difference in floating or settling speed, as shown in FIG. 3, for example. The layers are separated like this. That is, in Figure 3, the pigment with the highest sedimentation rate (white) is placed in the bottom layer A, the pigment with the next highest sedimentation rate (red) is placed in the upper layer, and the pigment with the next highest sedimentation rate (red) is placed in the bottom layer A. The pigments with the lowest sedimentation rate (blue + black) are separated into the top layer D. As shown in FIG.
5, each layer is extracted from the solid-liquid separator S ₁ ~
Send to _S5 . For example, the solid-liquid separator S ₁ contains a white pigment, S ₂ contains a reddish pigment, S ₃ contains a brownish yellow pigment, and S ₄ contains a yellowish pigment. A blue pigment is recovered, and a bluish black pigment is recovered in _S5 . The rising speed of the rising solvent is 0.05 to 1.0 mm/
sec range, but this rate of rise may vary depending on the hue, i.e. the flotation or sedimentation rate of each pigment, depending on the preferable rate, e.g.

[Table] There are pigments, and in order to achieve good layer separation of each hue,
Devices are devised to achieve the above-mentioned rising speed in each layer. That is, by making the dispersion column D a V-shaped column or by changing the inner diameter of the dispersion column D in stages, the above-mentioned rate of rise can be obtained in each layer. For example, if the pigment in the waste ink is a mixed pigment of white, red, yellow, blue, and black as described above, in order to separate the white color into the bottom layer and the blue and black layers into the top layer, the dispersion column D It is only necessary to set the cross-sectional area ratio of white = 1.00, red = 2.10, yellow = 3.65, and blue + black = 6.00. In addition, for the above-mentioned ascending solvent, the above-mentioned aromatic hydrocarbon and ester are mixed in advance and placed in one tank, and this is sent to the dispersion column D and circulated through the circulation line LO. Good, but
Since esters have good solubility (that is, they are compatible) with resins, they are extracted into the pigment recovery system together with the resins that are partially included in the recovered pigment (of course, aromatic hydrocarbons are also extracted). However, as shown in Figure 2, aromatic hydrocarbons and esters are are placed in tank T ₁ , and esters are placed in tank T _2.
The reduced amount of esters is replenished from line 1. The solvent from both tanks T ₁ and T ₂ is transferred to the flow control valve V _N
The flow rate is adjusted by the flowmeter F1, and the flow rate is measured by the flowmeter _F1 .
It is sent to the dispersion column D by pump P ₁ , and the circulation line
Cycled by LO. Further, as described above, the recovered pigment extracted into each of the solid-liquid separators S ₁ to _{S 5} is subjected to solid-liquid separation by standing, filtering, etc. in each of the solid-liquid separators S ₁ to _{S 5} . Note that f ₁ in each solid-liquid separator S ₁ to _{S 5} represents coarse particles of recovered pigment, and f ₂
is the fine particle and _f3 is the solvent. Next, an experimental example will be given to clarify the relationship between the rising rate of the ascending solvent in the dispersion column D and the hue of the recovered pigment. Experimental example Sample waste ink: red pigment (monoazore), blue pigment (phthalocyanine blue), yellow pigment (iron oxide yellow), white pigment (titanium white), black pigment (carbon black)
Mixed waste ink rising solvent: toluene/ethyl acetate = 25/75 (volume ratio), 20℃ Diameter and height of dispersion column D: 50mmφ, 800mmH Under the above conditions, the initial supply amount of waste ink was 200g
Then, layer separation and recovery were performed by sequentially changing the rate of rise of the rising solvent as follows in a batch test, and pigments with the following hues were recovered at each rate of rise.

【table】

[Table] White pigment remained at the bottom of dispersion tower D after each of the above pigments was recovered. When infrared spectroscopic analysis was performed on the pigment recovered at the speed of 0.35 to 0.40 mm/sec, the results shown in FIG. 4A were obtained. For reference, please refer to the fourth
Figure B shows the infrared absorption spectrum of nitrocellulose, and Figure 4C shows the infrared absorption spectrum of a new red pigment (monoazole). As is clear from Figures 4A to 4C, the recovered pigment contains nitrocellulose added as an impurity during the ink formulation stage, but from the color tone and the infrared absorption spectrum in Figure 4A, the infrared pigment ( It can be seen that monoazored) was recovered. That is,
In Fig. 4A, the typical absorption wavelength of the new red pigment (monoazored) shown in Fig. 4C is 1700 cm ^-1 ,
1470cm ^-1 , 1430cm ^-1 , 1320cm ^-1 , 1110cm ^-1 , 1010
A similar absorption spectrum appears at cm ^-1 etc. The method of the present invention described above can be applied not only to the recovery of pigments from waste ink but also to the separation and recovery of dyes having similar properties to pigments.

[Brief explanation of the drawing]

Fig. 1 is a diagram schematically showing the dispersion state of pigment particles in ink, Fig. 2 is a system diagram showing an embodiment of the method of the present invention, and Fig. 3 is a separation pattern in dispersion column D in Fig. 2. 4A to 4C are infrared absorption spectra of recovered pigment A, nitrocellulose B, and new pigment C.

Claims (1)

[Claims] 1. When recovering pigments from waste ink, a solvent that has poor pigment dispersibility but good solubility for resins is applied to the waste ink in an upward flow in the dispersion tower, and the liquid is dispersed due to the difference in the floating or settling speed of pigment particles. A method for recovering pigments by color from waste ink, which is characterized by sieving into multiple layers of each pigment and extracting and recovering each layer.